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Spending $50 for a "Manager" badge would do nothing to reduce spam. Are you aware of the amounts of money flowing through these campaigns and the people managing them?
This is indeed a very stupid suggestion. A single successful campaign could produce a hundred of these "managers".
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Well if the price for Manager badge is high, then bounty management would become centralized with very few trusted and reputable managers. Yes that would be good, but doing so will also make these managers to demand for higher pay rates. $50 is literally very low but having some kind of payment would be better.
No, it would not. As long as you have a small set of honest managers (i.e. non greedy), then that situation would remain fine. Most of the high rates nowadays come from fraudulent advertising, often off-site (plus they enroll their own army).